Angel 'Memo' Heredia, who has helped prepare Marquez to fight Manny Pacquiao, has been linked to performance-enhancing substances. But he says 'there's nothing to hide' in his work with Marquez.

Reporting from Las Vegas — Juan Manuel Marquez, 38, has ached for this third fight against Manny Pacquiao since his 2008 split-decision defeat by one point.

Marquez later boarded a flight to the Philippines, begging for another shot at Pacquaio. He watched bitterly as Pacquiao's purses skyrocketed in follow-up victories while Marquez was passed over.

On Saturday, Marquez gets his long-awaited shot at Pacquaio, and he has also drawn some scrutiny over how badly he wants to win.

At a news conference Wednesday, Marquez thanked a man who spent 11 weeks in training camp as his strength and conditioning coach: Angel "Memo" Heredia.

Last year, an independent arbitrator in Dallas assigned to determine penalties recommended by the U.S. Anti-Doping Agency issued a lifetime suspension of Jamaican track coach Raymond Stewart because his athletes used performance-enhancing drugs obtained by Heredia.

In his report, the arbitrator described Heredia as "an admitted drug dealer" who previously "identified two dozen elite athletes to whom he has provided performance-enhancing drugs." The report noted Heredia's father owned and operated a Mexico City drug laboratory.

"Stewart was provided [energy-boosting] EPO [and steroids] Winstrol, clenbuterol, dianabol, testosterone … over the period of their [1997 to 2004] association. 'Memo' testified that he advised Stewart what to take, what to provide to athletes he coached and how to get the [performance-enhancing drugs]."

Heredia received immunity from prosecution for his alleged drug distribution and money laundering by cooperating with the federal government and USADA.

Heredia says cooperating with the feds has kept him a law-abiding citizen, and his expertise has helped anti-doping agencies improve their testing methods over the past five years.

He said he works with at least five boxers, and has earned kinesiology and science degrees from Texas A&M Kingsville, with another science degree in Mexico.

Heredia says his goal with Marquez was to help him "legally" gain 10 pounds of strength for the 145-pound welterweight title bout against Pacquiao.

"There's nothing to hide," Heredia said. "The use of legal supplements — creatine, amino acids — has changed [Marquez]. It makes me a little mad someone's bringing my name up in a negative way….

"The last time he fought at this weight, he was slow, a guy who didn't lift weights. Now his reactions are quick, his punches are stronger."

Heredia put Marquez through "explosive" weightlifting sessions, high-intensity workouts and medicine ball training to build him up. The last time Marquez moved up in weight in 2009 he suffered a one-sided decision loss to Floyd Mayweather Jr.

Marquez praised Heredia as "a very good strength/conditioning trainer, which I needed."

Marquez has earned a heroic reputation in boxing by surviving three first-round knockdowns against Pacquiao in 2004 to claim a draw. Then Marquez won the 2009 fight of the year by dominating the younger Juan Diaz, and last year picked himself off the canvas again to knock out Michael Katsidis.

"I worked hard to get this [Pacquaio] fight, and I worked hard to win the fight, and that's all I'm concerned with," Marquez said.

Marquez learned of Heredia through his work with another Mexican champion, Jorge Arce.

"I'm grateful to what [Heredia] did," Marquez's trainer, Ignacio "Nacho" Beristain, said. "I've got a real strong fighter with a lot of energy because of it….

"I'm telling you, this guy [Marquez] would never do anything wrong. The eyes of the world are on him. Juan would never take anything like [performance-enhancing drugs]."

The Nevada State Athletic Commission will subject Marquez and Pacquiao to fight-night drug tests.

"I think these [fighters] are honorable people who won't do anything dishonest, no matter who's around them," Nevada State Athletic Commission Executive Officer Keith Kizer said of Marquez and Pacquiao. "It's unfortunate if they are hanging out with people with less than reputable pasts, but I'm not going to get into that guilt-by-association thing. We will test them."

Pacquiao was diplomatic about Heredia's involvement with Marquez. "We have a commission in Nevada," Pacquiao said. "I trust the commission."

Freddie Roach, Pacquiao's trainer, said of Marquez "putting on a lot of muscle, I absolutely love that. It'll make him slower."

"It's a real disrespect to [Marquez] who's been so honorable for so long, who's never been knocked down, to speculate like this about him," said Fernando Beltran, the Mexican promoter who helped Marquez get the Pacquiao fight. "He will never take a substance that's illegal, and it's irresponsible to assume that."